Protective effect of high density lipoprotein on endothelium-dependent vasodilatation

Low concentrations of high-density lipoprotein cholesterol (HDL-C) have bee n associated with increased risk of coronary heart disease (CHD) even when the total cholesterol (TC) and triglyceride (TG) levels are not elevated. T he mechanism by which HDL confers protection against atherosclerosis remain s speculative. Using high-resolution ultrasound, we measured the dilatation changes of brachial arteries during reactive hyperemia and after sublingua l glyceryl trinitrate (GTN) in 63 patients with established (CHD) and 45 co ntrols, in which the serum TC level was normal. The results showed that bot h flow-mediated dilatation (FMD) and GTN-induced dilatation of brachial art eries in patients with CHD were much reduced compared with control group (2 .3 1+2.46% vs. 7.43+/-4.10% and 16.41+/-6.15% vs. 22.44+/-8.63%, respective ly, P<0.001 for all). Univariate analysis indicated that FMD of brachial ar teries was inversely related to age (r=-0.226, P<0.05), hypertension (r=-0. 229, P<0.05), baseline diameter (r=-0.299, P<0.01) and LDL-C (r= -0.237, P< 0.05) and positively related to HDL-C (r=0.491, P<0.01). GTN induced vasodi latation was inversely related to age (r=-0.216, P<0.05) and baseline diame ter (-0.476, P<0.01). Multiple stepwise regression analyses in two groups t aken together showed that HDL-C and age were the independent predictors of the FMD of brachial arteries (beta=0.466, P=0.000 and beta=-0.184, P=0.020, respectively). Baseline diameter was significant predictor of GTN-induced vasodilatation (beta=-0.390, P=0.000). The analysis in the group of CHD pat ients showed that only HDL-C was significantly relate to the FMD of brachia l arteries (beta=0.295, beta=0.018) and in controls that hypertension and H DL-C were significantly relate to the FMD of brachial arteries (beta=-0.395 , P=0.004 and beta=0.344, P=0.011, respectively). These finding suggest tha t endothelium-dependent and endothelium-independent vasodilatation are impa ired in the patients with CHD. HDL exerts a protective effect on endotheliu m-dependent vasodilatation in TC being relatively normal population. (C) 20 00 Elsevier Science Ireland Ltd. All rights reserved.